The present invention relates to an image forming apparatus such as a copying apparatus, a printer or the like, in which a selectively set image is formed by a photoreceptive sheet coated with photosensitive microcapsules.
Such an image forming method is known in which a photoreceptive sheet coated with three kinds of photosensitive microcapsules containing colorless dyes of yellow, magenta and cyan and photo-setting materials sensitive to blue, green and red light, respectively is exposed by image forming exposure light having color information so as to form a selectively set image thereon and an image receiving sheet coated with developing materials for effecting color development of the colorless dyes is placed on the photoreceptive sheet so as to be pressed against the photoreceptive sheet such that a color image is formed on the image receiving sheet. By this known image forming method, a full-color image can be formed by a single exposure operation and thus, an image forming process can be simplified.
In the known image forming method, the above described three kinds of -photosensitive microcapsules have different photo-setting properties including photosensitivity, gamma characteristics, and, the like according to the kinds of photo-setting materials contained therein. Thus, the known image forming method has such a drawback that even when the three kinds of the photosensitive microcapsules have been exposed to an identical quantity of blue, green and red light, respectively, colors of a formed image have different densities due to differences in the photo-setting characteristics among the photosensitive microcapsules.
Thus, the present inventors have proposed in Japanese Patent Application No. 198746/1987, an auxiliary exposure device which is provided with three kinds of light source lamps for irradiating blue, green and red light, respectively. By this auxiliary exposure device, apparent photo-setting characteristics of the three kinds of the photosensitive microcapsules are made identical with one another and an excellent image can be obtained by correcting the colors of the formed image.
In this auxiliary exposure device, three kinds of tungsten lamps, such as a blue tungsten lamp (a lamp for irradiating white light), a green tungsten lamp and a red tungsten lamp are, respectively, provided with a filter permeable to blue light, a filter permeable to green light and a filter permeable to red light. Namely, the three kinds of the tungsten lamps are required to be provided for blue, green and red light, respectively and three control circuits are also required to be provided for the tungsten lamps, respectively. Hence, this auxiliary exposure device has such disadvantages that its manufacturing cost rises due to an increase in the number of its components and its structure becomes complicated. Meanwhile, even if LEDs or EL panels are employed in place of the above described lamps having the filters attached thereto, such inconveniences are incurred that the manufacturing cost rises due to an increase of the number of the lamps and the structure becomes complicated.